coresight: etb10: Make coresight_etb_groups static

Fix the following sparse warning:

drivers/hwtracing/coresight/coresight-etb10.c:720:30: warning: symbol
'coresight_etb_groups' was not declared. Should it be static?
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NMathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200518180242.7916-12-mathieu.poirier@linaro.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etb10.c

@@ -717,7 +717,7 @@ static const struct attribute_group coresight_etb_mgmt_group = {
 	.name = "mgmt",
 };
 
-const struct attribute_group *coresight_etb_groups[] = {
+static const struct attribute_group *coresight_etb_groups[] = {
 	&coresight_etb_group,
 	&coresight_etb_mgmt_group,
 	NULL,